Increased PM2.5 Caused by Enhanced Fireworks Burning and Secondary Aerosols in a Forested City of North China During the 2023–2025 Spring Festivals

Fireworks burning (FB) constitutes a major but short-lived source of PM_2.5 during the Chinese Spring Festival, significantly deteriorating air quality in certain regions. This study was conducted to evaluate its impact through real-time monitoring of PM_2.5 chemical compositions in a forestry city (Xinyang) during the pre-fireworks and fireworks periods at the Spring Festival of 2023-2025. During the fireworks period, PM_2.5 concentrations increased by 10.5-226.4% compared to pre-fireworks levels, of which the concentrations of secondary inorganic aerosols (SIA), K and Cl^- rose by 1.6-4.8, 1.9-14.7 and 1.5-8.1 times, and they accounted for 33.2-47.7%, 6.7-12.5% and 3.8-6.4% of PM_2.5, respectively. Correspondingly, PM_2.5/CO and SIA/CO ratios in 2023-2025 elevated by factors of 1.4-2.3 and 1.1-3.4, indicating distinct enhancements in secondary inorganic aerosols formation. Additionally, acidity of PM_2.5, RH and O_x also increased during fireworks. Collectively, higher sulfur and nitrogen oxidation ratios (SOR and NOR) during the fireworks period under the combined effects of high RH, O_x and acidity conditions indicated a greater conversion of secondary inorganic aerosols. Positive Matrix Factorization (PMF) analysis confirmed that FB and secondary aerosols (SA) source levels during fireworks increased by 2.5-19.3 and 1.9-4.4 times compared to pre-fireworks values. This study underscores the need for implementing stringent management of fireworks and secondary formation mitigation to reduce PM_2.5 concentrations during the Spring Festival.